This section discusses the different types of disk sets available in Solaris Volume Manager.
Each host has a local disk set. The local disk set consists of all the disks on a host that are not in a named disk set. A local disk set belongs exclusively to a specific host. The local disk set contains the state database for that specific host's configuration. Volumes and hot spare pools in the local disk set consist only of drives from within the local disk set.
In addition to local disk sets, hosts can participate in named disk sets. A named disk set is any disk set that is not in the local disk set. You can implement the following types of named disk sets to manage volumes, depending on the configuration of your system:
A shared disk set can be shared by multiple hosts. Although a shared disk set is visible from all the participating hosts, only the owner of the disk set can access it. Each host can control a shared disk set, but only one host can control it at a time. Additionally, shared disk sets provide a distinct namespace within which the volume is managed.
A shared disk set supports data redundancy and data availability. If one host fails, another host can take over the failed host's disk set. This type of configuration is known as a failover configuration.
Shared disk sets are intended, in part, for use with Sun Cluster or another supported High Availability (HA) framework. Solaris Volume Manager by itself does not provide all the functionality necessary to implement a failover configuration.
Before the autotake feature became available in the Solaris 9 4/04 release, Solaris Volume Manager did not support the automatic mounting of file systems on disk sets through the /etc/vfstab file. Solaris Volume Manager required the system administrator to manually issue a disk set take command by using the metaset -s setname -t command before the file systems on the disk set could be accessed.
With the autotake feature enabled, you can set a disk set to be automatically taken by a host at boot time. This feature allows you to define the mount options in the /etc/vfstab file for file systems on volumes in the enabled disk set.
Only single-host disk sets support the autotake feature. The autotake feature requires that the disk set is not shared with any other hosts. A disk set that is shared cannot be set to use the autotake feature. If the autotake feature is enabled on a shared disk set, the metaset -A command fails. However, after other hosts are removed from the disk set, the autotake feature can be enabled on the single-host disk set. Similarly, an autotake disk set cannot have other hosts added to it. However, if the autotake feature is disabled, additional hosts can then be added to the disk set.
In a Sun Cluster environment, the autotake feature is disabled. Sun Cluster handles the take and release of a disk set.
For more information on the autotake feature, see the -A option description in metaset(1M).
Starting with the Solaris 9 9/04 release, Solaris Volume Manager can manage storage in a Sun Cluster environment using multi-owner disk sets. Multi-owner disk sets allow multiple nodes in a cluster to share the ownership of disk sets and to simultaneously access the shared disks. All disks and volumes in a multi-owner disk set can be directly accessed by all the nodes in a cluster. Each multi-owner disk set contains a list of the nodes that have been added to the disk set. Consequently, each multi-owner disk set within a cluster configuration can have a different (and sometimes overlapping) set of nodes.
Each multi-owner disk set has a master node. The function of the master node is to manage and update the state database replica changes. Since there is a master node per disk set, multiple masters can exist simultaneously. There are two ways that the master is chosen. The first way is that a node becomes the master if it is the first node to add a disk to the disk set. The second way is when a master node panics and fails. The node with the lowest node id becomes the master node.
Multi-owner disk sets work with Sun Cluster and with applications such as Oracle9i Real Application Clusters. For information about compatible releases of Sun Cluster, see http://wwws.sun.com/software/cluster. For more information on Solaris Volume Manager for Sun Cluster, see Chapter 4, Solaris Volume Manager for Sun Cluster (Overview).